1. Field of Invention
This invention relates to a control system for a vehicle in which a fuel combustion-driven engine and a motor/generator are provided as interchangeable drive sources, and in which a transmission with a lock-up clutch is provided which is directly couplable between the drive sources and a drive wheel.
2. Description of Related Art
In a vehicle that has an engine, fuel is combusted within the engine, generating heat energy, and this heat energy is converted to mechanical energy (drive force) to drive the vehicle. With an engine, the driving region at which combustion efficiency is good and high torque can be obtained is limited to a relatively narrow r.p.m. range. Therefore, in a vehicle that uses an engine as the drive source, the engine r.p.m. and engine torque are changed by a transmission depending on a driving condition, and transmitted to the vehicle wheel(s).
Incidentally, in recent years, so-called hybrid vehicles have been proposed that have a different type of drive source, with objects of conserving the fuel which drives the engine, reducing the noise due to engine revolution, and reducing the exhaust gas that is generated through combustion of the fuel.
In these hybrid vehicles, too, a transmission is provided between the drive source and the drive wheel(s), but it is widely proposed to use a transmission with a torque converter, the same as is used in normal vehicles.
Additionally, there are many proposals to use a torque converter that is equipped with a directly couplable lock-up clutch, because the transmission efficiency in a conventional torque converter declines because fluid transmission is performed. For example, a hybrid vehicle disclosed in Japanese Laid-Open application 8-168104 also has a torque converter with a lock-up clutch as described above.